The present invention relates to the manufacture of silicon on insulator wafers, particularly to forming buried components, such as collectors, in such wafers, and more particularly to forming buried components in silicon-on-glass wafers and providing electrical contacts to the buried collectors using excimer laser technology.
Silicon-on-insulator (SOI) technologies have advanced dramatically in recent years towards the goal of producing thin single-crystal silicon (SCS) films on insulated substrates. Components such as metal-oxide-semiconductor transistors, fabricated in SOI films have the potential for increased mobility, reduced parasitic capacitance and leakage current as well as improved radiation hardness due to reduced junction sidewall area and elimination of bottom junction area. To date, there has been no success in achieving single-crystal silicon device fabrication on less expensive glass substrates capable of withstanding temperatures up to 600.degree. C. Others have achieved this with expensive glasses, such as Corning 1729 using 800.degree. C. (see L. J. Spankler et al., "A Technology for High-Performance Single-Crystal Silicon on Insulator Transistors", IEEE Electron Device Letters, Vol. 13, No. 4, April 1987, pp. 137-139) and Corning 1733 at 600.degree. C. with compromises (see U.S. Pat. No. 5,110,748 issued May 5, 1992 to K. Sarma). SOI transistors on glass substrates are particularly attractive for sensors and displays, although many other applications are possible such as actuators, high temperature electronics, optoelectronics, and radiation hard electronics.
A wide variety of techniques have been proposed for realizing thin silicon films compatible with high-performance devices on an insulating substrate. Due to the high temperature processing requirements of silicon (greater than 800.degree. C.), silicon-on-glass substrate processing has not been possible except on the so-called "high-temperature" glass, such as expensive Corning 1729 glass, capable of withstanding greater than 800.degree. C. temperatures. Other glasses used in commercial applications, such as lap-top displays, cannot withstand temperature exposures greater than 600.degree. C., such as the Corning 7059 or other "low-temperature" glasses. Due to the high temperatures of silicon processing, conventional techniques have relied on amorphous (a-Si) and polycrystalline (p-Si) materials which can be doped and treated at temperatures that the glass can withstand, but whose performance is decidedly inferior to crystalline films. These prior approaches to forming silicon-on-insulator substrates are exemplified by U.S. Pat. No. 5,013,681 issued May 7, 1991 to D. J. Godbey et al. and the following articles: "Nanosecond Thermal Processing For Ultra-High-Speed Device Technology", T. W. Sigmon et al., Materials Research Society Symp. Proc., Vol. 158, 1990, pp. 241-153; and "Low-Temperature Fabrication of p+-n Diodes with 300-.ANG. Junction Depth", K. H. Weiner et al., IEEE Electron Device Letters, Vol. 13, No. 7, July 1992, pp. 369-371.
Recently, a method has been developed for producing silicon microelectronics on glass substrates. However, this recent method utilizes laser activation for forming the doped and activated regions after thin silicon film formation and may optionally use etch stops between silicon layers and laser melting to smooth the silicon surfaces, and which is described and claimed in copending U.S. application Ser. No. 08/137,401, filed Oct. 18, 1993, entitled "A Method For Forming Silicon On A Glass Substrate", and assigned to the same assignee.
As pointed out above, there are substantial advantages for forming components, such as metal-oxide-semiconductor and bipolar transistors, on the SOI (silicon-on-glass) substrates. For this purpose there has been a need for a method for effectively forming buried components in SOI substrates. The present invention fills that need. Basically, the present Invention is directed to a method for introducing the buried components (collectors for example) prior to bonding the silicon to the glass substrate by masking the silicon surface to form a desired pattern and performing implantation, whereafter the silicon is bonded to the insulator (glass), or oxidized silicon substrate. The present invention additionally provides for the formation of electrical contact regions to the buried components by masking the silicon layer after it is bonded to the insulator, and laser melting regions of the silicon layer which contact the buried components.